The word "grats" or gratz is a truncated form of the word congratulations, or congratz. The word is used by people in online games (mainly mmorpg’s and mostly it is seen in PristonTale) its use is to congratulate someone on accomplishing something. I.e. moving up a level.

A man who goes beyond the ordinary. A stud in every form. May not be appreciated on the home front, but when he travels women flock to him. All men aspire to be g-rat, but none ever achieve it. G-Rat is a freak dancing champ. Not to be confused with g rat attack, a term used to describe a wannabe G-Rat who will never achieve that status.